Question

How many eggs are released by a human ovary in a month? How many eggs do you think would have been released if the mother gave birth to identical twins? Would your answer change if the twins born were fraternal?

Answer 1

Hint: The process of formation of the haploid egg or sperm cell from a diploid parent cell through meiosis is known as gametogenesis. The ovum or egg is a female gamete (the process is formation also known as oogenesis), while sperm is a male gamete (the process of formation is known as spermatogenesis).

Complete answer: Oogenesis or ovogenesis is a process of differentiation of a primary egg cell also known as ovum into a mature ovum. Primary egg cells are present in the female body even before the baby is born, i.e. in 8 to 20 weeks after a fetus has started to grow. There are around 400,000 primary egg cells present in ovaries. Oogenesis consist of three steps:
a) Multiplication phase: The cells from germinal epithelium in the ovaries divide to produce egg mother cells or oogonia that are larger than other cells.
b) Growth phase: The oogonia cell divides to form primary egg cells which are larger in size and can live for many years. Each primary egg cell is surrounded by granulosa cells to form a primary follicle that provides nutrition to the primary egg cell.
c) Maturation phase: The primary egg cell undergoes two divisions; first meiotic division and second meiotic division to form egg cells. In a month, a human female releases one egg cell. If a mother gives birth to identical twins, then the zygote formed after fertilization is divided into two identical cells that have developed into individual embryos. Thus, only one egg is released. When two separate eggs are fertilized by two sperms, two separate zygotes are produced and such twins are known as fraternal twins.

Note: Identical twins are also known as monozygotic twins and they share same genes and are usually of the same-sex, whereas fraternal twins are known as dizygotic twins and can be of different sex. A human female can give birth to more than two offspring either identical or fraternal. This is termed polyzygotic (birth from more than two zygotes).